Plasma processing apparatus and plasma processing method

ABSTRACT

The plasma processing apparatus has a plasma processing chamber where plasma processing of the sample is performed, and plasma power supply that supplies radio frequency electric power for generating plasma. The radio frequency electric power is time modulated by a pulse wave having a first period and a second period that are repeated periodically. The pulse wave of the first period has first amplitude and the pulse wave of the second period has second amplitude which is a limited value smaller than the first amplitude. The extinction of the plasma, which is generated during the first period having the first amplitude, is maintained during the second period having the second amplitude with a predetermined dissociation.

BACKGROUND OF THE INVENTION

The present invention relates to a plasma processing apparatus and aplasma processing method suitable for plasma processing using pulsedischarge.

Mass-production of three dimensional structure transistors calledFin-FET (Fin Field Effect Transistor) are beginning with themicronization of semiconductor devices. To manufacture this kind ofsemiconductor devices, a dry etching technology is required to satisfy afurther micronization, a higher aspect, and a highly precise etching fora complicated profile which is not seen in the conventional twodimensional transistors.

For example, an etching domain becomes smaller when a trench of a linereaches a certain depth during a dummy gate etching of Fin-FET. Usually,the area between the lines becomes the etching domain; however, in thiscase, a narrow area surrounded by the exposed Fin and the line turns tobe the etching domain. A broader process window is therefore requiredfor the plasma processing apparatus for a dry etching for such profile.

One technology for realizing a highly precise plasma etching is a plasmaetching method using pulse discharge. For example, JP-A-H09-185999discloses a method for controlling density and composition of radicalby: measuring the density and composition of radical generated bydecomposition of plasma reactant gas; pulse modulating the electricpower of a plasma generation apparatus with a constant cycle and;controlling duty ratio of the pulse modulation based on the measuredresult.

U.S. Pat. No. 6,489,245 B discloses a method for reducing a maskcorrosion during the etching by alternating high electric power cycleand low electric power cycle of discharge electric power with a certainpulse frequency such that a polymer accumulates on the mask during thelow electric power cycle.

JP-A-2010-021442 discloses a method for forming a via of high aspectratio on a silicon substrate by: supplying alternately the high electricpower and low electric power to an antenna; forming protective film withsputtering during the high electric power period; performing etchingprocessing during the low electric power period and; repeating theetching process and the protective film formation process alternately.

JP-A-H08-045903 discloses a method for performing a clean andreproducible etching so as to prevent an adsorption and deposition of anetching reaction product on a wall face of a processing chamber bymodulating ON/OFF of both the bias electric power and the dischargeelectric power, but not turning both of them ON at the same time.

SUMMARY OF THE INVENTION

In the etching processing using pulse discharge disclosed in eachliterature above, plasma is generated during the etching, in otherwords, highly dissociated plasma is utilized for etching.

Therefore, in order to realize an etching processing adaptable forforming a three dimensional device such as Fin-FET, where the etchingarea becomes smaller due to change of etching domain or the aspect ratiobecomes higher during the etching, the control of the radical depositionis important which largely effects the control of vertical profile.However, the process window for controlling the amount of radicaldeposition is not sufficient.

Specifically, in the device using ECR discharge disclosed inJP-A-H09-185999, the adjustment of the adherence probability of radicaldeposition is not sufficient because high density plasma that is highlydissociated is generated, and is difficult to generate lowly dissociatedplasma.

The purpose of the present invention is to provide a plasma processingapparatus and the method that can broaden the process window bycontrolling the plasma dissociation.

Another purpose of the present invention is to provide an etchingprocessing apparatus and an etching method that is adaptable formicrofabrication etching and can perform vertical etching even when anetching surface has a difference between isolation pattern and densepattern.

Another purpose of the present invention is to provide an etchingprocessing apparatus and an etching method that is adaptable for anetching where the etched profile turns smaller during its process.

The above object of the present invention can be achieved by providing aplasma processing apparatus including: a plasma processing chamber thatgenerates plasma inside and performs plasma processing of a sample; apower supply for plasma generation that supplies radio frequencyelectric power for generating the plasma; a bias power supply, arrangedinside the plasma processing chamber, that supplies radio frequencyelectric power for bias to a sample stand for mounting the sample; and acontroller, wherein the controller is configured to time modulateperiodically the radio frequency electric power for generating theplasma using a pulse wave of first period and a pulse wave of secondperiod, wherein the pulse wave of the first period supplies radiofrequency electric power of first amplitude capable of generating theplasma, and wherein the pulse wave of the second period supplies radiofrequency electric power of second amplitude smaller than the firstamplitude capable of maintaining after-glow of the plasma, time modulateperiodically the radio frequency electric power for the bias between anelectric power supplying period and an electric power terminatingperiod, adjust the electric power supplying period of the radiofrequency electric power for the bias to the second period of the radiofrequency electric power for generating the plasma, and control theelectric power supplying period of the radio frequency electric powerfor the bias so as to be shorter than the second period.

Another object of the present invention can be achieved by providing aplasma processing method wherein gas inside a processing chamber isturned to plasma periodically, and a sample inside the processingchamber is processed using the plasma, including: supplying alternatelya first radio frequency electric power value for turning the gas intoplasma and a second radio frequency electric power value for maintainingafter-glow of the plasma generated by the first radio frequency electricpower value in an arbitrary state periodically, the second radiofrequency electric power value being smaller than the first radiofrequency electric power value; and supplying bias power for enteringion of the after-glow state into the sample while the second radiofrequency electric power value is supplied.

The present invention allows broadening the process window bycontrolling the plasma dissociation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view illustrating a plasma etchingapparatus according to the present invention;

FIG. 2 is a timing chart illustrating supply of plasma power and biaspower according to the present invention;

FIG. 3 is a figure illustrating a relation between a saturation ioncurrent density and a time during a plasma generation;

FIG. 4 is a figure illustrating a saturation ion current density when apulsed plasma power is turned ON/OFF;

FIG. 5 is a timing chart illustrating a supplying state of plasma powerand bias power according to the plasma processing method (Table 1) of afirst embodiment of the present invention;

FIG. 6 is a longitudinal sectional view illustrating an etching profileof a sample processed by the etching condition of Table 1 using theelectric power of FIG. 5;

FIG. 7 is a timing chart illustrating a supplying state of the plasmapower and the bias power of Table 2 according to a comparative exampleof the first embodiment of the present invention;

FIG. 8 is a longitudinal sectional view illustrating an etching profileof a sample processed by the etching condition of Table 2 using electricpower of FIG. 7;

FIG. 9 is a timing chart illustrating a supplying state of plasma powerand bias power according to the plasma processing method (Table 3) of asecond embodiment of the present invention;

FIGS. 10A to 10C are longitudinal sectional views illustrating anetching profile of a sample processed by the etching condition of Table3 using electric power of FIG. 9;

FIG. 11 is a timing chart illustrating a supplying state of the plasmapower and the bias power of Table 4 according to a comparative exampleof the second embodiment of the present invention;

FIGS. 12A and 12B are longitudinal sectional views illustrating anetching profile of a sample processed by the etching condition of Table4 using the electric power of FIG. 11;

FIG. 13 is a timing chart illustrating an example of a control method ofbias power according to the present invention;

FIG. 14 is a timing chart illustrating another example of a controlmethod of the bias power according to the present invention; and

FIG. 15 is a timing chart illustrating another supplying method of theplasma power and the bias power according to the present invention.

DESCRIPTION OF THE EMBODIMENTS

The present invention relates to a plasma processing apparatus and amethod that can perform a lowly dissociated plasma processing. Theinvention will be discussed first with reference to FIG. 1 through FIG.4.

FIG. 1 illustrates a magnetic field microwave plasma etching apparatusas an example of the plasma processing apparatus of the presentinvention. A sample stand 103 for arranging a wafer 102, which is asample, is arranged inside a chamber 101 that forms a plasma processingchamber, where the room is decompressed by exhausting the gas. A waveguide tube 105 and a magnetron 106 oscillating a microwave are arrangedin this order on the upper opening of the chamber 101 intervening amicrowave transmission window 104.

A first radio frequency power supply 113, which is a power supply forplasma generation for supplying radio frequency electric power, isconnected to the magnetron 106. A solenoid coil 107 for forming amagnetic field inside the chamber 101 is provided in the perimeter ofthe chamber 101 and the wave guide tube 105. A gas introduction port 111is connected to the chamber 101, and a gas for etching processing issupplied from a processing gas supplying apparatus (not illustrated).The processing gas supplied into the chamber 101 is excited by aninteraction between a microwave electric field from the magnetron 106and a magnetic field from a solenoid coil 107 to form plasma 112 insidethe chamber 101.

The chamber 101 has a wafer conveyance port 110 for carrying in/out thewafer 102. The wafer 102 is carried into the chamber 101 by a conveyingapparatus (not illustrated) through the wafer conveyance port 110. Thewafer 102 is arranged on the sample stand 103. The sample stand 103 isarranged with a static electricity zipper for holding the wafer byabsorption and is connected with a static electricity adsorption powersupply 108. The sample stand 103 is also connected with a second radiofrequency power supply 109, which is bias power supply for introducingion inside the plasma into the plasma processing wafer. The bias powersupply is controlled so that voltage between bias peaks of the radiofrequency electric power applied to the sample stand becomes constantduring an electric power supplying period.

The first radio frequency power supply 113 and the second radiofrequency power supply 109 are connected with a controller 114, and arecontrolled radio frequency electric power outputs respectively. Asillustrated in FIG. 2, the controller 114 can control the pulse-outputof plasma generation electric power and bias power. The applying timingof one of the electric powers can be delayed, and each electric powercan be synchronized. The controller also has a delay circuit that delaycontrols the start of the electric power supplying period of the radiofrequency bias power against a second period of the radio frequencyplasma generation electric power.

The controller turns OFF the output of the bias power supply when thevoltage between the bias peaks of the radio frequency electric powersupplied to the sample stand reaches a predetermined value. FIG. 2 (a)illustrates a pulse wave for controlling an output value and an outputtiming from the first radio frequency power supply 113. One cycle of thepulse wave includes “high period” where a high output value ismaintained and “low period” where a small output value is maintained.These two periods are repeated alternatively.

FIG. 2 (b) illustrates a pulse wave for controlling an output value andan output timing from the second radio frequency power supply 109. Thepulse wave is synchronized with the plasma power pulse and a bias powerpulse is generated following the end of the high period of a cycle withdelay of Δt. The bias power pulse is generated only during the lowperiod of the plasma power pulse.

FIG. 2 (a) illustrates the plasma power pulse wave in solid line and thecorresponding saturation ion current in dashed line that is measured onthe wafer. The plasma power during the high period allows plasmaignition, and the saturation ion current increases rapidly during thisperiod. FIG. 3 illustrates a saturation ion current density. The currentdensity increases with the plasma ignition and approaches to a saturatedstate in about 0.1 ms, and reaches the saturation state substantially inabout 0.4 ms. This indicates that the high ion-density plasma, or highelectron density plasma can be obtained when the high period is setwithin 0.1 ms to 0.4 ms.

The electron acts on plasma dissociation. During the high period, ahighly dissociated plasma can be obtained because a radio frequencyelectric power with high power is supplied to the plasma, which will bethe energy for raising plasma dissociation in the electron, and theelectron temperature is increased. When the pulse output during the highperiod is terminated, the saturation ion current starts decreasingbecause plasma power is no longer supplied as illustrated in FIG. 4.Generally, the plasma turns substantially to an extinguished state inabout 0.2 ms, although it depends on a saturation ion current densityvalue, a kind of gas, and an existence of magnetic field when the plasmais generated.

A plasma state so called after-glow is seen before the saturation ioncurrent becomes zero, i.e., the plasma extinguishes. In the after-glowstate, plasma dissociation decreases as the time elapses. Conceptually,in case of a methane (CH4) gas, when the saturation ion current is inthe state (i) where the plasma power is in ON (high) period asillustrated in FIG. 4, the collision frequency of the gas and theelectron increases and the dissociation progresses such as to CH+3H.

In the state (ii), where the plasma power is in OFF period, thecollision frequency of the gas and the electron decreases, and lowlydissociated substance such as CH2+2H increases. In state (iii), wherethe plasma power is in OFF period, the collision frequency of the gasand the electron decreases further, and further lowly dissociatedsubstance such as CH3+H increases. In state (iv), where the plasma poweris in OFF period, the collision frequency of the gas and the electronfurther decreases, and substance such as CH4 increases which is same tothe gas condition during the supplying period.

The saturation ion current density is high immediately after the end ofthe high period. After a certain time has elapsed, the dissociation isdecreased and the saturation ion current density decreases to less thanhalf. In the present embodiment, the plasma power pulse, which iscontrolled to a low power such that the plasma does not ignite, isoutput from the controller 114 to the first radio frequency power supply113 after the high period as illustrated in FIG. 2. As a result, a lowlydissociated plasma can be maintained, where the saturation ion currentvalue is in a predetermined range, without extinguishing the after-glow.

When a lowly dissociated plasma is maintained during the low periodwhere a low power plasma power pulse is output, (in other words, whenthe saturation ion current value is in predetermined value or lessduring the low period), a pulse signal is output from the controller 114to the second radio frequency power supply 109 so as to apply bias powerto the sample stand 103 from the second radio frequency power supply109.

The wafer 102 can thereby be plasma processed with the lowly dissociatedplasma. The ion in the after-glow state can be affected by the biaspower, where the ion is in arbitrary dissociated plasma state, bycontrolling the delay time Δt for allowing a use of plasma suitable forprocessing a target object. Further, an impedance matching of the biaspower applied from the second radio frequency power supply 109 isperformed by a matching unit (not illustrated) when the plasma of thelow period turns stable.

The first embodiment of the present invention will be discussed withreference to FIG. 5 and FIG. 6.

Etching processing of Poly-Si film using a device illustrated in FIG. 1under conditions shown in Table 1 will be discussed.

TABLE 1 etching time 32 sec processing gas CL2 O2 HBr Ar + CH4processing pressure 0.3 Pa plasma power/duty/time high period 750W/15%/0.15 ms low period 200 W/85%/0.85 ms bias power/duty low period120 W/80%

In this case, a mixed gas of Cl2, O2, HBr, and Ar+CH4 gases is used as aprocessing gas for the etching processing. In this gas system, a methane(CH4) gas is mixed to prevent a side etching of a side wall of thePoly-Si film. The microwave power for plasma generation is set to highand low values and are time modulated and supplied alternatively asshown in FIG. 5. The parameters of the microwave power are 750 W and 200W each having duty of 15% and 85% and frequency is 1 kHz as shown inTable 1.

In the present apparatus, the 2.45 GHz microwave is used as plasma powersource, and plasma is ignited when the output is approximately 400 W ormore. The bias power is synchronized with the plasma power withfrequency of 1 kHz so that the bias power is supplied only during a lowperiod of the plasma power, and is supplied with duty of 80%. In thiscase, the delay time Δt is 0.05 ms.

FIG. 6 illustrates a sectional view of the wafer which is etch processedunder the conditions mentioned above. In this case, the wafer has astructure where an oxide film 202 of 5 nm, a Poly-Si film 203 of 50 nm,and a nitride film mask 204 of 10 nm are accumulated on a Si substrate201. FIG. 6 is a sectional view of lines and spaces of Poly-Si filmafter the etching. The etching progresses during the low periodaccording to the etching processing of the present embodiment.

The plasma power during the low period is 200 W where the plasma isunable to be generated and maintained with an ordinary continuousdischarge. However, the plasma generated in the high period can bemaintained for a short period until the next high period. During thislow period, low plasma density can be maintained.

If the plasma density is low, the collision frequency of an electron anda radical decreases. As a result, CH3 becomes a dominant radical in theplasma with a comparatively low adhesion coefficient. When the adhesioncoefficient is low, the radical does not adhere to the surface firstlanded to, and the radical tends to go toward the rear side of the line.The amount of the radical adhesions in the interval area of the lines ofthe Poly-Si film 203 become closer between the broader area and thenarrower area. As a result, a vertical profile is obtained in the sidewall having a broader space facing the line. In other words, the outerside surface of the line is prevented from being thick as illustrated inFIG. 6.

As a comparative example of the first embodiment of the presentinvention, an etching processing of the similar Poly-Si film underconditions shown in Table 2 will be discussed.

TABLE 2 etching time 19 sec processing gas CL2 O2 HBr Ar + CH4processing pressure 0.3 Pa plasma power/duty/time 750 W/100% biaspower/duty 120 W/100%

Compared to the etching processing of the first embodiment, the plasmapower and the bias power are not time modulated in this comparativeexample, and are supplied continuously as illustrated in FIG. 7.Therefore, the etching of the Poly-Si film progresses continuously andthe etching time becomes shorter compared with the first embodiment.

FIG. 8 illustrates a sectional view of the wafer which is etch processedunder the conditions mentioned above. Since the components having thesame reference number as in the FIG. 6 are the same, the detaileddescription are omitted. In the present comparative example, the plasmapower is large when bias power is applied for etching processing andplasma density becomes large during this period. In this gas system, amethane (CH4) gas is mixed for reducing the side etching of the Poly-Sifilm side wall as discussed above.

Therefore, the number of CH radicals with high adhesion coefficient(radicals with large number of unconnected bonds) increases when theplasma density is high. This is because the collision frequency of themethane gas and the electron increases and a dissociation progressessuch as from CH4 to CH+3H. When there are many high adhesive coefficientradicals, a tapered profile as illustrated in FIG. 8 is made. This isbecause the collision frequency of the radical increases at the sidewall of the line having a broader space facing the side wall of thePoly-Si film 203, and this side wall facing the broader space becomesthicker.

Therefore, the first embodiment allows an etching processing with lowlydissociated plasma and can control the adhesive probability of theaccumulative radicals. This is because the plasma in the after-glowstate, where the plasma is generated during the high period, can be usedfor the processing. Therefore, the adhesive condition of theaccumulative radical can be optimized even when the etching object has alarge difference between isolation pattern and dense pattern in the linewidth, and allows a vertical etching processing of the side walls of thelines having a difference between isolation pattern and dense pattern.

As discussed above, the process window of the processing apparatus canbe broadened even when the processing using an ordinary plasmageneration is difficult. This is because a lowly dissociated plasma canbe used for the processing. The broadened process window allows anetching processing with a sufficient profile control.

Further, according to the first embodiment, the after-glow state duringan unstable period, where the plasma is extinguishing, can be maintainedstably. This is because a predetermined plasma power, which is smallerthan that of high period, is supplied during the low period in theafter-glow state of plasma generated during the high period. Thisstabilizes an etching processing which is performed by applying biaspower during the low period.

The use of a magnetic field microwave plasma processing apparatus, asthe plasma processing apparatus, allows processing under a high vacuumcondition compared with the capacitive coupling method or the inductiveconnection method plasma processing apparatus because this apparatus cangenerate ECR plasma. The high vacuum state is advantageous for usingafter-glow state plasma because the collision probability of ions andradicals is less.

The ECR plasma allows broadening the range of the saturation ion currentdensity between the high state and the low state because the ECR plasmacan form a high-density plasma compared with the other types of plasma.In other words, setting range of the electric power output value for thelow period, which is used for plasma processing, can be broadened, andthe processing window can thereby be broadened.

A second embodiment of the present invention will be discussed withreference to FIG. 9 and FIGS. 10A to 10C.

An etching processing of three dimensional structure Fin-FET using theapparatus illustrated in FIG. 1 under conditions of Table 3 will bediscussed. In this case, the Fin-FET has a structure where an oxide film302 of 5 nm, a Poly-Si film 304 of 150 nm, and a nitride film 305 of 10nm are accumulated on a Si substrate 301 as illustrated in FIG. 10. ThePoly-Si film 304 is layered so as to range over the Fin 303 on the oxidefilm 302. FIG. 10B is a figure viewed from the direction A in the FIG.10A, and FIG. 10C is a figure viewed from the direction B in the FIG.10A.

TABLE 3 step No. 1 2 3 4 etching time 6 sec 16 sec 170 sec 30 sec proc-CL2 ∘ ∘ ∘ ∘ essing O2 — — ∘ — gas CO2 ∘ ∘ — ∘ HBr ∘ ∘ ∘ ∘ Ar + CH4 — — ∘— processing pressure 0.3 Pa 0.3 Pa 0.4 Pa 0.1 Pa plasma power/duty/ 750W/50% 750 W/50% high period 600 W/ time 750 W/ 100% 15%/0.15 ms — — lowperiod — 200 W/ 85%/0.85 ms bias power/duty 300 W/40% 300 W/40% lowperiod 40 W/ 120 W/80% 50%

The etching processing consists of four steps in this case. Cl2, O2,CO2, HBr, and Ar+CH4 gases are used as the processing gases, and mixtureof these processing gases are used in each step as indicated in Table 3.In this gas system, a methane (CH4) gas is mixed for reducing the sideetching during the etching as necessity.

Table 3 indicates the value of the microwave power used for plasmageneration in each step. FIG. 9 illustrates the supply timings of themicrowaves. In Step 1, a natural oxidation film is removed. In Step 2,the Poly-Si film 304 is etched until the Fin 303 exposes. In Steps 1 and2, as illustrated in FIG. 9 (a), the ON/OFF of the plasma power and thebias power are pulse controlled synchronously with frequency of 1 kHzand duty ratios of 50% and 40% respectively.

In Step 3, the Poly-Si film 304 is etch processed below the exposed partof the Fin 303. As illustrated in FIG. 9 (b), the bias power is appliedsynchronizing the low period of the plasma power in Step 3. The plasmapower is set to high and low values and are time modulated and suppliedalternatively. The parameters of the plasma power are 800 W and 200 Weach having duty of 15% and 85% and the frequency is 1 kHz. In thepresent apparatus, the 2.45 GHz microwave is used as the plasma power,and the plasma is ignited when the output is approximately 400 W or morein this case. The bias power is synchronized with the plasma power withfrequency of 1 kHz so that the bias power is supplied only during a lowperiod of the plasma power, and is supplied with duty of 50%.

The delay time Δt of the bias power pulse is 0.05 ms in this case. InStep 4, an over-etching is performed for removing a residual substance.In Step 4, as illustrated in FIG. 9 (c), the plasma power is continuousand the bias power is pulse controlled (ON/OFF controlled) with pulsecycle of 1 kHz and duty of 50%.

FIGS. 10A to 10C illustrate sectional views of the wafer which is etchprocessed under the conditions mentioned above. According to the etchingprocessing of the second embodiment, the circumference environment ofthe etching domain changes largely. That is, when the Fin 303 startsexposing by the etching process of Step 2, the etching area of thePoly-Si film 304 turns to an area excluding the area of Fin 303, whilethis area was not excluded from the etching area of the Poly-Si film 304before the exposure of the Fin 303.

In the Step 3, a dense portion surrounded by the Poly-Si film 304 andthe Fin 303 is etched as illustrated in FIG. 10C. The aspect ratiotherefore becomes much larger and the etching environment changeslargely compared to the environment in Step 2. Thus, the etchingcondition needs to be changed to a condition suitable for a narrowdomain etching.

The etching profile is effected largely by the difference betweenisolation pattern and dense pattern of the lines when the Fin 303 isexposed. This is because the etched domain, or the etching space,becomes further narrower. In Step 3, the bias power is set small toprevent the Fin 303 from being sputter etched. Thus, protection of theside walls becomes important because the nature of the isotropic etchingshall be considered. However, for purpose of decreasing the adhesioncoefficient of the accumulative radical and supplying the radical to anarrow space and a deep space, the lowly dissociated plasma in theafter-glow is maintained during the low period, after the plasma isgenerated in the high period.

The plasma power during the low period is 200 W, where the plasma isunable to be generated and maintained with an ordinary continuousdischarge. However, the plasma generated in the high period can bemaintained for a short period until the next high period. During thislow period, low plasma density can be maintained. The bias power issupplied in the low period and the etching progresses during the lowperiod.

This reduces the difference between the sparse portion, where thedeposition is likely to occur, and the dense portion where thedeposition hardly occurs. The excessive deposition in the sparse portionis thereby inhibited and this affords a vertical etching. Thus, thethree dimensional Fin-FET can be etch processed with a sufficientlycontrolled profile.

As a comparative example of the second embodiment of the presentinvention, an etching processing of the similar three dimensionalFin-FET, under conditions shown in Table 4, will be discussed.

TABLE 4 step No. 1 2 3 4 etching time 6 sec 16 sec 86 sec 30 sec procCL2 ∘ ∘ — ∘ essing- O2 — — ∘ ∘ gas CO2 ∘ ∘ — — HBr ∘ ∘ ∘ ∘ Ar + CH4 — —∘ — processing pressure 0.3 Pa 0.3 Pa 0.4 Pa 0.1 Pa plasma power/duty/750 W/50% 750 W/50% 750 W/15% 600 W/ time 100% bias power/duty 300 W/40%300 W/40% 120 W/80% 40 W/ 50%

The process in Step 3 is different compared to the etching processing ofthe second embodiment. However, the other steps, i.e., Steps 1, 2, and 4are similar to that of the second embodiment, and the detaileddescription will be omitted.

In Step 3, the plasma power is time modulated with ON/OFF as illustratedin FIG. 11 at switching frequency of 1 kHz and with duty ratio of 50%,and the plasma power is not time modulated with high and low values. Thebias power is synchronized with the plasma power, and is time modulatedso that the bias power is turned ON when the plasma power is ON atswitching frequency of 1 kHz and with duty ratio of 50%.

FIGS. 12A and 12B illustrate sectional views of the wafer which is etchprocessed under the conditions mentioned above. Since the componentshaving the same reference number as in the FIGS. 10A to 10C are thesame, the detailed description will be omitted. In the presentcomparative example, the plasma power is large when bias power isapplied for etching processing in Step 3, and plasma density becomeslarge during this period. In this gas system, a methane (CH4) gas ismixed for reducing a side etching of the Poly-Si film side wall asdiscussed above.

Therefore, the number of CH radicals with high adhesion coefficient(radicals with large number of unconnected bonds) increases when theplasma density is high. This is because the collision frequency of themethane gas and the electron increases and a dissociation progressessuch as from CH4 to CH+3H. When there are many high adhesive coefficientradicals, a tapered profile as illustrated in FIG. 12A is made. This isbecause the collision frequency of the radical increases at the sidewall having a broader space facing the side wall of the Poly-Si film304, and this side wall becomes thick.

According to the second embodiment, in addition to the advantage of theprevious embodiment, there is an advantage that an etching processingwith a lowly dissociated plasma is possible even in the threedimensional Fin-FET. This allows a control of the adhesive probabilityof the accumulative radicals and enables a vertical etching of thePoly-Si film without damaging the Fin even when the Fin is exposed.

In the above embodiments, the bias power pulse of a constant value isoutput so as to output the bias power of constant power. FIG. 13 is atiming chart illustrating a relation between a plasma power pulse, avoltage between bias peaks (referred to “Vpp” hereafter), and a biaspower pulse. During the low period of the plasma power, although theafter-glow is not extinguished, the saturation ion current decreasesgradually. When a constant power source is used for supplying the biaspower during this low period, the Vpp increases with the decrease of thesaturation ion current.

The etching characteristic changes when the Vpp changes largely becausethe ion energy entering the wafer is substantially proportional to theVpp. Therefore, the second radio frequency power supply 109 can beturned OFF by the controller 114, when the upper limit (Vmax) of the Vppis determined and the Vpp reaches the Vmax, other than setting the dutyratio of the bias power. The etching characteristic can thereby bestabilized even when the Vpp changes.

Another control method of the bias power will be discussed withreference to FIG. 14. FIG. 14 is a timing chart illustrating therelation between a plasma power pulse, a voltage between bias peaks(Vpp), and a bias power pulse. In contrast to FIG. 13, the Vpp iscontrolled to a constant value in FIG. 14. In this case, the controller114 reduces the bias power corresponding to the decrease of thesaturation ion current density, while the bias power pulse is ON forpreventing the increase of the Vpp and controlling Vpp to a constantvalue. This allows a further stabilization of the etchingcharacteristics because the Vpp, which effects the etchingcharacteristics, can be kept constant.

In the above embodiments, a plasma etching apparatus using a magneticfield microwave source is employed. However, it cannot be overemphasizedthat the present invention can be applied for a plasma processingapparatus that uses the other type of plasma generating method such asthe capacitive coupling type plasma source and the inductive couplingtype plasma source. It is effective for obtaining the plasma of highgeneration efficiency and maintaining a long glow-discharge to form amagnetic field in a processing chamber during the plasma generation andto act the magnetic field.

In the present embodiment, the etching processing of the sample is madeby entering the ion of lowly dissociated plasma into the wafer bysupplying the bias power only during the low period of the plasma power.However, if the etching profile allows or the wafer damage is allowable,the bias power can be supplied also during the high period of the plasmapower as illustrated in FIG. 15. In this case, the bias power outputvalue can be set adequately according to the content of the processingduring the high period and does not have to be adjusted with the biaspower value of the low period. By doing so, the etching processing timecan be shortened.

Similarly, if the etching profile allows or the wafer damage isallowable, an etching processing can be made by alternating a time wherebias power is supplied only during the high period of the plasma power,and a time where bias power is supplied only during the low period ofthe plasma power, every 10 seconds.

The present invention allows a processing using the dissociated plasmaof a desired degree and can broaden the process window. The inventionalso allows a microfabrication etching, and allows a vertical etchingeven when the etching surface has a difference between isolation patternand dense pattern. The invention also allows an etching processing whichis affordable even when the etched profile changes further smallerduring the etching.

As mentioned above, the stability (reproducibility) of the processing isimproved by alternatively performing a plasma processing during a lowperiod supplied by bias power, and a plasma processing during a highperiod supplied by bias power. This is because a stable plasmaprocessing during the high period is added to the processing.

The invention claimed is:
 1. A plasma processing apparatus comprising: aplasma processing chamber in which a sample is plasma-processed; a firstradio frequency power supply that supplies a first radio frequencyelectric power for generating plasma, the first radio frequency electricpower being pulse-modulated with a first pulsed waveform having a firstperiod and a second period; a sample stage on which the sample ismounted; a second radio frequency power supply that supplies a secondradio frequency electric power to the sample stage, the second radiofrequency electric power being pulse-modulated with a second pulsedwaveform having an on period and an off period; and a controllerconfigured to: control the first radio frequency power supply to supplythe first radio frequency electric power during the first period togenerate the plasma and the first radio frequency electric power duringthe second period to maintain after-glow of the plasma without ignitingthe plasma; control a predetermined time delay between a start of thesecond period and a start of the on period; control the second period soas to include the on period; control the first radio frequency electricpower during the second period so as to be greater than the second radiofrequency electric power during the on period; control the second radiofrequency electric power so as to only be supplied during the secondperiod; and control to turn off output of the second radio frequencypower supply when a peak-to-peak voltage of a radio frequency voltageapplied from the second radio frequency power supply during the onperiod reaches a predetermined value.
 2. The plasma processing apparatusaccording to claim 1, wherein the time delay is 0.05 milliseconds. 3.The plasma processing apparatus according to in claim 1, wherein thepredetermined value the controller is configured to control to turn offoutput of the second radio frequency power supply when the peak-to-peakvoltage of the radio frequency voltage applied from the second radiofrequency power supply during the on period reaches is an upper limit(Vmax), which is the predetermined value.
 4. The plasma processingapparatus according to claim 1, wherein the off period includes thefirst period.
 5. A plasma processing apparatus comprising: a plasmaprocessing chamber in which a sample is plasma-processed; a first radiofrequency power supply that supplies a first radio frequency electricpower for generating plasma, the first radio frequency electric powerbeing pulse-modulated with a first pulsed waveform having a first periodand a second period; a sample stage on which the sample is mounted; asecond radio frequency power supply that supplies a second radiofrequency electric power to the sample stage, the second radio frequencyelectric power being pulse-modulated with a second pulsed waveformhaving an on period and an off period; and a controller configured to:control the first radio frequency power supply to supply the first radiofrequency electric power during the first period to generate the plasmaand the first radio frequency electric power during the second period tomaintain after-glow of the plasma; control the second period so as toinclude the on period; control the off period so as to include the firstperiod; and control the second radio frequency electric power so as toonly be supplied during the second period; and control to turn offoutput of the second radio frequency power supply when a peak-to-peakvoltage of a radio frequency voltage applied from the second radiofrequency power supply during the on period reaches a predeterminedvalue.
 6. The plasma processing apparatus according to claim 5, whereinthe controller is further configured to control a period of the firstperiod so as to be smaller than a period of the second period.
 7. Theplasma processing apparatus according to in claim 5, wherein thepredetermined value is an upper limit (Vmax).
 8. A plasma processingapparatus comprising: a plasma processing chamber in which a sample isplasma-processed; a first radio frequency power supply that supplies afirst radio frequency electric power for generating plasma, the firstradio frequency electric power being pulse-modulated with a first pulsedwaveform having a first period and a second period; a sample stage onwhich the sample is mounted; a second radio frequency power supply thatsupplies a second radio frequency electric power to the sample stage,the second radio frequency electric power being pulse-modulated with asecond pulsed waveform having an on period and an off period; and acontroller configured to: control the first radio frequency power supplyto supply the first radio frequency electric power during the firstperiod to generate the plasma and the first radio frequency electricpower during the second period to maintain after-glow of the plasmawithout igniting the plasma control the second period so as to includethe on period; control the second radio frequency electric power so asto only be supplied during the second period; control a period of thefirst period so as to be smaller than a period of the second period; andcontrol to turn off output of the second radio frequency power supplywhen a peak-to-peak voltage of a radio frequency voltage applied fromthe second radio frequency power supply during the on period reaches apredetermined value.
 9. The plasma processing apparatus according toclaim 8, wherein the controller is further configured to control the offperiod so as to include the first period.
 10. The plasma processingapparatus according to claim 8, wherein the controller is furtherconfigured to control a period of the first period so as to be smallerthan a period of the on period.
 11. The plasma processing apparatusaccording to claim 10, wherein the controller is further configured tocontrol a period of the on period so as to be longer than a period ofthe off period.
 12. The plasma processing apparatus according to claim11, wherein the controller is further configured to control a period ofthe second period so as to be longer than a period of the off period.13. The plasma processing apparatus according to in claim 8, wherein thepredetermined value is an upper limit (Vmax).